1. Field of the Invention
The present invention relates to a push button switch of the water, oil and dust proof type.
2. Prior Art
The push button switch having such arrangement as shown in FIG. 1, for example, has been well known as the conventional one of the water proof type. This push button switch is also of the illuminant type and its operation plunger system is divided to upper and lower plungers 1 and 2. When the upper plunger 1 is removed from the case 3, the light source can be exchanged.
The reason why water proofness is needed in the case of the push button switch having such arrangement as described above is that water and others must be prevented from entering into the switch section located in the lower portion of the case 3 through between the case 3 and the operation section including the operation plungers and located in the upper portion of the case 3. A clearance is needed between the operation section and the case 3 because the operation section is arranged to come into and out of the case, and when water and others enter into the switch section through the clearance, the switch section is made inoperative. In order to prevent this, the rubber seal 5 is interposed between the lower plunger 2 and the case 3 in the case of the conventional push button switch having the arrangement as shown in FIG. 1. The rubber seal 5 is a ring having a reversed U-shape in section, and its outer circumferential rim is fixed to the case 3 by the fastening ring 6 while its inner circumferential rim to the groove 2a on the upper face of the lower plunger 2. When assembly is finished, the inner circumferential rim of the rubber seal 5 is forcedly engaged with the groove 1a on the underside of the upper plunger 1. When the upper plunger 1 is pushed down, the lower plunger 2 is moved against the compression coil spring 7 to render the switch section operative. These movements of the operation plungers 1 and 2 are allowed by the transformation of the rubber seal 5, and sealing between the operation plungers 1, 2 and the case 3 can be guaranteed by the rubber seal 5 in spite of the movements of the operation plungers 1 and 2.
In the case of the conventional push button switch having the above-described arrangement, however, the sealing capacity between the operation plungers 1, 2 and the rubber seal 5 becomes insufficient to lower the water proofness when the upper plunger 1 is attached slant to or insufficiently forced into the lower plunger 2. Sufficient sealing capacity can be achieved when the inner circumferential rim of the rubber seal 5 is fixed to the outer circumference of the upper plunger 1, but when it is arranged like this, the upper plunger 1 cannot be detached from the case 3.